Multicopter with boom-mounted rotors

ABSTRACT

A multicopter aircraft with boom-mounted rotors is disclosed. The multicopter includes a fuselage; a port side wing coupled to the fuselage; and a starboard side wing coupled to the fuselage. Each of the wings has mounted thereto one or more booms, each boom having a forward end extending forward of a corresponding wing to which the boom is mounted and an after end extending aft of said corresponding wing to which the boom is mounted. The aircraft further includes a first plurality of lift rotors, each rotor in said first plurality being mounted on a forward end of a corresponding one or said booms; and a second plurality of lift rotors, each rotor in said second plurality being mounted on an after end of a corresponding one or said booms. Each rotor produces vertical thrust independent of the thrust produced by the other rotors.

BACKGROUND OF THE INVENTION

Multicopter aircraft typically include a plurality of horizontallyoriented rotors, sometimes referred to as “lift fans,” to provide lift,stability, and control. A flight control system, sometimes referred toas a “flight controller” or “flight computer”, may be provided totranslate pilot or other operator input, and/or corrections computed byan onboard computer, e.g., based on sensor data, into forces and momentsand/or to further translate such forces and moments into a set ofactuator (e.g., lift rotors; propellers; control surfaces, such asailerons; etc.) and/or associated parameters (e.g., lift fan power,speed, or torque) to provide the required forces and moments.

For example, pilot or other operator inputs may indicate a desiredchange in the aircraft's speed, direction, and/or orientation, and/orwind or other forces may act on the aircraft, requiring the lift fansand/or other actuators to be used to maintain a desired aircraftattitude (roll/pitch/yaw), speed, and/or altitude.

An aircraft typically is considered to have six degrees of freedom ofmovement, including forces in the forward/back, side/side, and up/downdirections (e.g., Fx, Fy, and Fz) and moments about the longitudinal(roll) axis, the transverse (pitch) axis, and the vertical (yaw) axis(e.g., Mx, My, and Mz). If an aircraft has more actuators than degreesof freedom, it must be determined how the various actuators will be usedto act on the aircraft in response to commands received via manualand/or automated controls. For a given set of one or more pilot commandsunder given circumstances, some combinations of actuators capable ofacting on the aircraft to achieve the result indicated by the pilotcommand(s) may be more effective and/or efficient than others. Forexample, some may consume more or less power and/or fuel than others,provide a more smooth transition from a current state than others, etc.

Rotors may spin at a high rate and could pose a risk to an occupant of amanned multicopter and/or to equipment housed in a fuselage or otherstructure comprising the multicopter.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a block diagram illustrating an embodiment of a flight controlsystem.

FIG. 2A is a block diagram illustrating an embodiment of a multicopteraircraft with angled rotors.

FIG. 2B is a block diagram showing a front view of the multicopteraircraft 200 of FIG. 2A.

FIG. 2C is a block diagram illustrating an example of angled rotors asimplemented in an embodiment of a multicopter aircraft with angledrotors.

FIG. 2D is a block diagram illustrating a top view of an embodiment of amulticopter aircraft with angled rotors.

FIG. 2E is a block diagram illustrating an example of forces and momentscapable of being generated by angled rotors in an embodiment of amulticopter aircraft with angled rotors.

FIG. 2F is a block diagram showing a side view of the multicopteraircraft 200 of FIG. 2A.

FIG. 2G is a block diagram showing a side view of the multicopteraircraft 200 of FIG. 2A.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

A multicopter aircraft with angled rotors is disclosed. In variousembodiments, a multicopter aircraft as disclosed herein includes aplurality of lift fans or other rotors disposed in a configurationaround a fuselage and/or other centrally-located structure of theaircraft. In some embodiments, a first subset of the rotors may bedisposed on a one side of the aircraft and a second subset of the rotorsmay be disposed on an opposite side of the aircraft. In variousembodiments, each of at least a subset of the rotors is mounted at acorresponding non-zero angle off of a horizontal plane of the aircraft.In some embodiments, the angle at which each rotor is mounted isdetermined at least in part by a location of the rotor relative to thefuselage and/or a human or other occupied portion thereof, the anglebeing determined at least in part to ensure that a plane in which therotor primarily rotates does not intersect the fuselage and/or a humanor other occupied portion thereof. In various embodiments, therespective angles at which at least a subset of the rotors are mountedmay be determined at least in part to provide the ability to generatelateral force components in the horizontal plane of the aircraft atrotor mount locations that are offset in the horizontal plane from acenter of gravity of the aircraft, so as to provide an ability to usethe rotors to control yaw of the aircraft (i.e., rotation about avertical axis of the aircraft) by applying moments about the verticalaxis.

FIG. 1 is a block diagram illustrating an embodiment of a flight controlsystem. In the example shown, flight control system 100 includes asource of flight control inputs 102 configured to provide flight controlinputs 104 to a controller 106, e.g., a flight control computer. In someembodiments, source of inputs 102 may comprises one or both of pilotinput, e.g., via manual flight controls, and auto-pilot or otherself-piloting technologies. For example, in a self-piloting aircraftinputs 104 may be generated by a self-piloting program/computer 102. Invarious embodiments, source of inputs 102 may include manual inputdevices (sometimes referred to as “inceptors”), such as stick, throttle,rudder, collective, joystick, thumb stick, and/or other manualcontrol/input devices configured to be manipulated by a pilot or otheroperator to control the flight of an aircraft. Such inceptor devicesand/or associated electronics, and/or a self-piloting program, computer,or module, may be configured to provide as input signals 104 one or moreof a roll direction, roll rate, yaw direction, yaw rate, pitch angle,pitch rate, altitude, altitude rate and/or forward or other thrust inputsignal. In the example shown, controller 106 also receives sensor data118, e.g., wind speed, air temperature, etc., from sensors 116. Flightcontroller 106 translates, aggregates, and/or otherwise processes and/orinterprets the received flight control inputs 104 and/or sensor data 118to generate and provide as output associated forces and/or moments 108to be applied to the aircraft via its control assets (e.g., propellers,rotors, lift fans, aerodynamic control surfaces, etc.; sometimesreferred to herein as “actuators”) to maneuver the aircraft in a mannerdetermined based at least in part on the flight control inputs 104and/or sensor data 118. In various embodiments, forces/moments 108 mayinclude forces and/or moments along and/or about one or more axes of theaircraft, such as x, y, and z axes, corresponding to longitudinal,transverse, and vertical axes of the aircraft, respectively, in variousembodiments.

Referring further to FIG. 1, the flight control system 100 includes anonline optimizer/mixer 110 configured to receive forces/moments 108.Online optimizer/mixer 110 receives as input forces/moments 108 andcomputes dynamically (online) a set of actuators and associatedcommands/parameters 112 to achieve the requested forces/moments 108. Insome embodiments, the optimizer minimizes total power given a desiredcombination of forces and moments. Actuators 114 are configured tooperate in response to actuator commands/parameters 112 provided byonline optimizer/mixer 110.

In the example shown, sensors 116 provide sensor data 118 to onlineoptimizer/mixer 110. Examples of sensors 116 and/or sensor data 118 mayinclude one or more of airspeed, temperature, or other environmentalconditions; actuator availability, failure, and/or health information;aircraft attitude, altitude, and/or other position information;presence/absence of other aircraft, debris, or other obstacles in thevicinity of the aircraft; actuator position information; etc. In variousembodiments, online optimizer/mixer 110 may be configured to take sensordata 118 into account in determining an optimal mix of actuators andassociated parameters to achieve a requested set of forces and moments.For example, in some embodiments, six or more lift fans may be providedto lift an aircraft into the air, enable the aircraft to hover, controlaircraft attitude relative to the horizontal, etc. In some embodiments,failure of a lift fan may be reflected in sensor data 118, resulting ina seamless response by online optimizer/mixer 110, which provides anoptimal set of actuators and parameters 112 that omits (does not relyon) the failed lift fan. Likewise, in some embodiments, sensor datareflecting diminished power/performance, overheating, etc., may be takeninto consideration, such as by adjusting a mapping of actuator parameterto expected effect on the aircraft for affected actuators.

FIG. 2A is a block diagram illustrating an embodiment of a multicopteraircraft with angled rotors. In various embodiments, a flight controlsystem such as flight control system 100 of FIG. 1 may be embodied in anaircraft such as aircraft 200 of FIG. 2A. In the example shown, aircraft200 includes a fuselage (body) 202 and wings 204. A set of threeunderwing booms 206 is provided under each wing. Each boom 206 has twolift fans 208 mounted thereon, one forward of the wing and one aft. Eachlift fan 208 may be driven by an associated drive mechanism, such as adedicated electric motor. Each lift fan 208 produces vertical thrustindependent of the thrust produced by the other lift fans 208. One ormore batteries (not shown) and/or onboard power generators (e.g., smallgas turbine) may be used to drive the lift fans 208 and/orcharge/recharge onboard batteries.

In various embodiments, each boom 206 is positioned at an angle relativeto a vertical axis of the aircraft such that the lift fans 208 aremounted thereon at an associated angle, as described more fully inconnection with FIGS. 2B-2E.

In the example shown in FIG. 2A, a propeller 210 is mounted on thefuselage 202 and configured to push the aircraft through the air in theforward (e.g., x axis) direction. The propeller 210 is positionedbetween a pair of tail booms 212 that extend aft and are joined at theiraft end by a tail structure on which aerodynamic control surfacesincluding elevators 216 and rudder 218 are mounted. In variousembodiments, each of the inboard booms 206 forms at least in part anintegral part of the corresponding port/starboard side tail boom 212. Insome embodiments, the tail booms 212 comprise extensions aft from therespective inboard booms 206. For example, the tail booms 212 may beformed as part of or fastened (e.g., bolted) to an aft end of thecorresponding inboard boom 206. Additional control surfaces includeailerons 214 mounted on the trailing edge of wings 204.

In the example shown, four ailerons 214 are included, e.g., to provideredundancy. In some embodiments, if a single aileron 214 is lost orfails the remaining three ailerons 214 are sufficient to control theaircraft. Likewise, in some embodiments, loss of one rudder 218 resultsin one remaining rudder to provide a degree of yaw control, along withthe lift fans. Finally, in some embodiments four elevators 216 areprovided for loss/failure tolerance.

In some embodiments, an aircraft 200 as shown in FIG. 2A may have thefollowing approximate dimensions:

Wingspan: 36.0 feet Nose to tail 21.4 feet Centerline to first boom 6.1feet Distance between inner booms 12.2 feet Spacing between booms (samewing) 4.0 feet Push propeller sweep 6.5 feet Lift fan sweep 4.2 feetDistance between fan centers (same boom) 8.7 feet

FIG. 2B is a block diagram showing a front view of the multicopteraircraft 200 of FIG. 2A. Coordinate axes in the z (vertical) and y(side) direction are indicated. The front view shown in FIG. 2Billustrates the respective angles off the vertical axis (z axis aslabeled), sometimes referred to herein as “cant angles”, at which theoutboard, middle, and inboard pairs of lift fans 206 are oriented. Invarious embodiments, angling the lift fans, as indicated, may provideadditional options to control the aircraft, especially at or near hover.For example, different combinations of fans may be used to exercise yawcontrol (e.g., rotate around z axis), to slip sideways or counteract theforce of wind while in a hover (y axis), etc.

In various embodiments, the respective angles at which lift fans 208 maybe oriented may be determined based at least in part on safetyconsiderations, such as to increase the likelihood that debris throwncentrifugally from a lift fan, e.g., should the lift fan break apart,would be propelled on a trajectory and/or in a plane that does notintersect a human-occupied portion of fuselage 202. In some embodiments,two side by side seats are provided for passengers in a forward part offuselage 202. Batteries to power the lift fans 208 and/or push propeller210 may be located in a central/over wing part of the fuselage 202, andin some embodiments both the human-occupied and battery occupied partsof the fuselage are protected at least in part by canting the booms/liftfans as disclosed herein.

In some embodiments, lift fan cant angles may be determined at least inpart via a constrained optimization design process. The fan cants (e.g.,roll and pitch fan angles) may be determined by an optimization processin which an object is to minimize the amount of torque required by anyindividual motor for a variety of trimmed or equilibrium conditionsincluding: angular accelerations, any individual fan failure,crosswinds, and center of gravity variations. In some embodiments, theoptimization is subject to constraints of preventing the plane of thefan blade from intersecting the crew in the event of catastrophicfailure of a fan. Another example of a constraint that may be applied isensuring that the fans are aligned to the local flow angle for forwardflight with the fans stopped and aligned with the boom.

In various embodiments, the effective forces and moments capable ofbeing provided by each respective lift fan may be stored onboard theaircraft 200 in a memory or other data storage device associated withthe onboard flight control system. In various embodiments, a matrix,table, database, or other data structure may be used.

In some embodiments, effectiveness under different operating conditionsmay be stored. For example, effectiveness of a lift fan or controlsurface may be different depending on conditions such as airspeed,temperature, etc. In some embodiments, forces and moments expected to begenerated by a lift fan or other actuator under given conditions may bediscounted or otherwise reduced, e.g., by a factor determined based atleast in part on an environmental or other variable, such as a measureof lift fan motor health.

In an aircraft having angled lift fans as in the example shown in FIG.2B, the forces and moments capable of being generated by a given liftfan may reflect the angle at which each lift fan is mounted. Forexample, lift fans mounted at an angle relative to the horizontal planeof the aircraft would generate a horizontal force component and avertical force component, and each force may generate a correspondingmoment about one or more axes of the aircraft, depending on the locationat which the fan is mounted relative to the center of gravity of theaircraft.

FIG. 2C is a block diagram illustrating an example of angled rotors asimplemented in an embodiment of a multicopter aircraft with angledrotors. In the example shown, the approximate angles at which the leftside (as viewed from the front) rotors of the aircraft 200 as shown inFIGS. 2A and 2B are mounted are shown. In particular, the left most(outboard) lift fan is shown to be mounted at an angle θ1 to thevertical (and, therefore, horizontal/lateral) axis of the aircraft,tilting away from fuselage 202, resulting in a plane of rotation of thelift fan, indicated by the dashed arrow extending away from the liftfan, not intersecting the fuselage 202. In some embodiments, the planeof rotation may intersect the fuselage but not a human-occupied orotherwise critical portion thereof.

Similarly, in the example shown the middle lift fan and the inboard liftfan have been angled in towards the fuselage 202, resulting in theirrespective planes of rotation being rotated downward by correspondingangles, such that they do not intersect the fuselage 202.

In various embodiments, angling lift fans or other rotors towards oraway from a fuselage or critical portion thereof, and/or other criticalstructures, may decrease the risk that debris thrown centrifugally fromthe rotor would hit the fuselage or other structure.

FIG. 2D is a block diagram illustrating a top view of an embodiment of amulticopter aircraft with angled rotors. Specifically, in FIG. 2D a topview off aircraft 200 of FIG. 2A is shown. Coordinate axes in the x(forward) and y (side) direction are indicated. In the example shown,the aircraft 200 includes twelve lift fans 208, six on either side ofthe fuselage 202. On each side of the fuselage 202, three lift fans aremounted forward of the wing 204 and three aft. The lift fans 208 aremounted in pairs on corresponding booms 206 mounted under the wings 204.The outermost booms are tilted away from the fuselage 202 and the middleand inner booms are tilted towards the fuselage, as shown in FIGS. 2Band 2C.

FIG. 2E is a block diagram illustrating an example of forces and momentscapable of being generated by angled rotors in an embodiment of amulticopter aircraft with angled rotors. In FIG. 2E, the fuselage 202 ofthe aircraft 200 of FIG. 2D is shown to have a center of gravity 220.The circles in FIG. 2E each represent a corresponding one of the liftfans 208. The arrows labeled F_(y1), F_(y2), etc. represent therespective lateral (y-axis) components of the force generated by theangled lift fans 208 by virtue of their being mounted at angles, andshown in FIGS. 2A-2D. The rear (aft) fans are shown to be mounted at anx-axis distance x₁ from center of gravity 220. As a result, the y-axiscomponents of the rear lift fans, as shown, would result incorresponding moments of magnitudes proportional to the distance x1being applied to the aircraft about the vertical axis (z-axis, using theconvention shown in FIGS. 2A-2E). The moment contributed by any givenone of the rear lift fans would be determined by the lift forcegenerated by the lift fan as actuated by the flight control system, withthe direction (counter-clockwise or clockwise) depending on the positionof the lift fan and whether it was tilted away from or towards thefuselage 202. For example, the rear leftmost lift fan would contribute alateral force F_(y1) resulting in contributing a counter-clockwisemoment component about the center of gravity 220. The right side (asshown in FIG. 2E) rear inner and middle lift fans (F_(y4), F_(y5))similarly would contribute a counter-clockwise moment component. Bycontrast, the lift fans associated with lateral force components F_(y2),F_(y3), and F_(y6) would contribute clockwise moment components.

Similar to the rear lift fans, the forward lift fans (associated withlateral force components F_(y7)-F_(y12), in this example) wouldcontribute moment components proportional to the x-axis distance x₂ atwhich they are mounted relative to the center of gravity 220.

In various embodiments, the respective lift fans 208 may be rotated inalternating clockwise or counterclockwise rotations, e.g., to balanceside forces associated with rotation direction. In the example shown inFIGS. 2A-2E, a total of twelve lift fans 208 are included. In variousembodiments, an even number of lift fans including at least four liftfans may be included and distributed evenly on each side of thefuselage. Upon loss or failure of a lift fan, a corresponding lift fanon an opposite side of the aircraft may be de-activated, to maintainbalance. For example, loss of a clockwise rotating lift fan on a forwardend of an innermost boom on a port side of the aircraft may result in acounterclockwise rotating lift fan in a complementary position on theopposite side, such as the aft end of the innermost boom on the oppositeside, may be shut down and omitted from use (e.g., zero RPM/torque addedas a constraint for that lift fan) in subsequent optimizationcomputations to determine mixes of actuators and associated parametersto achieve desired forces and moments.

FIG. 2F is a block diagram showing a side view of the multicopteraircraft 200 of FIG. 2A. In the example shown, the lift fans 208 aremounted at a prescribed forward tilt relative to a horizontal plane ofthe aircraft 200. The booms 206 are shown to be mounted substantiallyaligned with the horizontal plane of the aircraft 200 when in levelflight. The wings 204 sweep up slightly as they extend away from thefuselage 202. In various embodiments, the angle at which the lift fans208 are tilted forward may be determined at least in part on the sameconsiderations as the angles illustrated in FIGS. 2B and 2C, i.e., toensure that debris thrown centrifugally from a lift fan if it were tobreak apart would not intersect at least a human-occupied or otherwisecritical portion of a cockpit or cabin portion of fuselage 202. In someembodiments, the angle at which the lift fans 208 are tilted forward maybe selected at least in part to minimize drag, turbulence, or otherundesirable aerodynamic effects of the lift fans when the aircraft 200is in forward flight, e.g., being propelled by push propeller 210.

FIG. 2G is a block diagram showing a side view of the multicopteraircraft 200 of FIG. 2A. In the example shown, approximate airflowpatterns are illustrated by arrows 242 and 244. Arrow 242 shows airflowing with minimal resistance over the forward lift fans 208 and, duein part to the forward tilt of the forward lift fans 242, continuingrelatively unimpeded over wing 204, and clearing the aft lift fans 208(or, in some embodiments, flowing over them in a relatively low dragpath, due in part to their forward tilt). Arrow 244 shows air flowingunder/through the forward lift fans 208, under the wing 204, and flowingover the aft lift fans 208 in a relatively low drag manner, due at leastin part to the forward tilt of the aft lift fans 208.

In some embodiments, the wing 204 may not sweep upward to the sameextent as shown in FIGS. 2F and 2G, and in some such embodiments the aftlift fans may be more within a same horizontal plane as the forward liftfans 208 and wing 204. In some such embodiments, the aft lift fans 208may be tilted back slightly, instead of forward, to provide acontinuous, relatively low drag pathway for air to flow over the forwardlift fans 208, the wing 204, and the after lift fans 208, e.g., when theaircraft 200 is in forward flight mode.

In various embodiments, a flight control system, such as flight controlsystem 100 of FIG. 1, is configured to determine a mix of actuators andcorresponding actuator parameters, including of lift fans 208, toachieve required forces and moments, including by taking intoconsideration the moments about the z-axis that would be generated andapplied to the aircraft 200 by virtue of the lift fans being mounted atangles, as disclosed herein.

In various embodiments, techniques disclosed herein may be used toprovide a multicopter aircraft having angled lift fans and/or rotors.Each rotor may be mounted at an angle such that debris throwncentrifugally from the lift fan, in a plane of rotation of the lift fan,would not intersect the fuselage or other critical structure of theaircraft. In various embodiments, angling rotors as disclosed herein mayprovide a degree of authority over (ability to control or influence) yawof the aircraft, e.g., during hover or vertical takeoff (lift) orlanding operations.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. An aircraft, comprising: a fuselage; a port sidewing coupled to the fuselage; a starboard side wing coupled to thefuselage; wherein each of said wings has mounted thereto two or morebooms, each boom having a forward end extending forward of acorresponding wing to which the boom is mounted and an after endextending aft of said corresponding wing to which the boom is mounted; afirst plurality of lift rotors, each rotor in said first plurality beingmounted on the forward end of a corresponding one of said booms; and asecond plurality of lift rotors, each rotor in said second pluralitybeing mounted on the after end of the corresponding one of said booms;wherein each rotor in said first plurality and each rotor in said secondplurality produces an amount of vertical thrust independent of levels ofvertical thrust produced by the other rotors; wherein a first subset ofsaid booms each is mounted to said port side wing or said starboard sidewing at a non-zero angle relative to a substantially vertical axis ofthe aircraft such that the boom is tilted inboard towards the fuselage;and wherein a second subset of said booms each is mounted to said portside wing or said starboard side wing at a non-zero angle relative tothe substantially vertical axis of the aircraft such that the boom istilted outboard away from the fuselage.
 2. The aircraft of claim 1,wherein the port side wing and the starboard side wing each has threebooms mounted thereto and wherein the first plurality of lift rotors is6 and the second plurality of lift rotors is
 6. 3. The aircraft of claim1, wherein the lift rotors in the first and second plurality of liftrotors are driven by electric motors.
 4. The aircraft of claim 1,wherein the port side wing and the starboard side wing comprise a singlewing structure mounted to the fuselage such that said port said wingcomprises a port side portion of said single wing structure extending tothe port side of the fuselage and said starboard said wing comprises astarboard side portion of said single wing structure extending to thestarboard side of the fuselage.
 5. The aircraft of claim 1, furthercomprising a split boom structure extending aft from each of an inboardpair of said booms, the split boom structure comprising a port side boomand a starboard side boom extending aft of the fuselage and being joinedat an after end of the split boom structure by a tail structure.
 6. Theaircraft of claim 5, wherein each of said booms comprising the inboardpair of booms forms at least in part an integral part of a correspondingone of said port side boom and said starboard side boom.